Search

Micro/nanochannels are considered as a promising method to enhance heat transfer due to the large ratio of surface area to the volume. To clarify the optimization direction of micro/nanochannel walls, the convective heat transfer of nanochannels under different surface coupling characteristics are explored with molecular dynamics. Specifically, the effects of solid-liquid interaction, wall atomic vibration property, rough morphology and their interactions on heat transfer and hydrodynamic characteristics of nanochannels are investigated based on orthogonal test method. The results show that the solid-liquid interaction and vibration frequency of wall atoms are the two most important factors affecting Nusselt number and comprehensive performance coefficient. Strengthening the vibrational coupling between wall atoms and liquid atoms is critical for promoting heat transfer. Unlike this, the two most significant factors influencing friction factor are solid-liquid interaction and rough morphology. The increase in static structure factor of liquid leads to an increase in its microstructural orderliness, which is the fundamental reason for the decrease of slip length and subsequently leads to an increase in the friction factor. Taking into account the heat transfer and flow resistance characteristics, the optimal combination of wall surface characteristics composed of the solid-liquid interaction, vibration frequency of wall atoms and roughness factor has been selected, which can achieve the best overall heat transfer performance of nanochannels. [Display omitted] • Some mechanisms that occur in nanochannel convective heat transfer are revealed. • Effect of surface characteristics coupling on flow and heat transfer is explored. • The priority order of influencing factors is determined by orthogonal test method. • Optimal combination of surface characteristics for nanochannel wall is proposed. • The optimal combination provides a reference for structural optimization design. [ABSTRACT FROM AUTHOR]

• Influence mechanism of solid–liquid interaction is revealed via molecular dynamics. • The relationship between Nusselt number and temperature jump length is determined. • The relationship between fRe and normalized slip length is proposed. • Solid-liquid interaction improves overall heat transfer within a certain range. • The present work provides a new insight for the effect of solid–liquid interaction. Nanochannel cooling technology is widely used in the heat dissipation systems of various micro/nanoscale electronic devices or components. The consideration of resistance loss and the optimization of heat dissipation are of great significance for the widespread application of nanochannel cooling technology. A model of convective heat transfer in nanochannel with constant wall temperature is established with molecular dynamics method. The effects of solid–liquid interaction on flow and heat transfer characteristics are investigated. The microscopic mechanisms of the solid–liquid interaction influencing heat transfer performance and flow resistance of nanochannel are explored from the atomic level. The results show that the enhancement of the solid–liquid interaction leads to the increases of the coupling degree of vibration frequency between wall and liquid atoms and the orderliness of microstructure of first fluid layer, and finally facilitates heat transfer between nanochannel wall and liquid. The Nusselt number in nanochannel is not a constant and decays exponentially with the increase of temperature jump length. Meanwhile, as the solid–liquid interaction increases, the slip length decreases and the friction factor increases, which are attributed to the augment of the static structure factor, resulting in more fluid atoms in near-wall region are firmly locked by the wall. The friction factor in nanochannel not only depends on the Reynolds number, but also is closely related to the slip length. To further evaluate overall heat transfer performance of the nanochannel that considers flow resistance, the comprehensive performance coefficient is discussed. It's found that the solid–liquid interaction is effective in improving the overall heat transfer performance of the nanochannel within a certain range. [ABSTRACT FROM AUTHOR]

• Flow resistance of convective heat transfer in rough nanochannel is probed. • Weak wall-fluid interaction is conducive to drag reduction but not to heat transfer. • Smaller free shear ratio is beneficial for heat transfer and drag reduction jointly. • Optimum heat transfer performance is achieved at shear free ratio of 0.1875. As an efficient cooling method, the convective heat transfer in nanochannel has been widely utilized in thermal management of various energy systems. However, the effects of surface roughness on velocity slip and flow resistance in nanochannel are still unclear. The effects of rough morphology and wall-fluid interaction on the flow and thermal characteristics in rectangular nanochannel are probed with molecular dynamics method. The results show that nanostructure morphology and wall-fluid interaction induce distinct variations in temperature jump and velocity slip, which further determine the heat and momentum exchange between the channel wall and fluid. Specifically, rough morphology is responsible for the augments of heat transfer and flow resistance, which is derived from limitation on the motion of fluid atoms by the nanostructure grooves in channel. In comparison, the strong wall-fluid interaction brings about the improvement of heat transfer and the increase of flow resistance, which owes to the adsorption enhancement. As the nanostructure free shear ratio increases from 0.1875 to 0.75, the flow resistance increases and heat transfer performance weakens. Yet, the combination of rough morphology and wall-fluid interaction is significant for overall heat transfer performance. The overall heat transfer performance in rough channel with the weak wall-fluid interaction is superior. The Nusselt number in rough channel only decreases by 1.78% while the resistance coefficient reduces by 27.1%. The optimal overall performance is achieved in rough channel with the nanostructure free shear ratio of 0.1875. [ABSTRACT FROM AUTHOR]

• Nanoscale convective heat transfer considering flow resistance is investigated. • Combing weak wall-fluid interaction with roughness helps synthesis performance. • Smaller morphology period outperforms other periods in rough nanochannel. • Dense rough morphology is beneficial for heat transfer and drag reduction jointly. Convective heat transfer of hot fluid flowing through a cold parallel plate nanochannel with constant wall temperature is investigated with molecular dynamics. The effects of surface properties including rough morphology and wall-fluid interaction on the heat transfer and flow characteristics are probed. Different surface wettability characterized by the strong and weak wall-fluid interaction as well as five rough morphologies corresponding to various nanostructure morphology periods, are considered. It is noteworthy that the rough morphology and wall-fluid interaction are key parameters for affecting the flow and heat transfer characteristics. The results show that flow resistance and Nusselt number decrease with the increase of rough morphology period as well as the decrease of wall-fluid interaction. Under the same wall-fluid interaction, the best heat transfer enhancement in rough channel is obtained at the morphology period of 12 Å, while a minimum flow resistance in rough channel is obtained at the morphology period of 48 Å. Another novelty finding is that the combination of surface rough morphology and weak wall-fluid interaction will bring a favorable impact on the heat transfer enhancement and drag reduction. Under the weak wall-fluid interaction, the synthesis performance coefficient corresponding to the rough morphology period of 12 Å is highest among all considered rough morphologies, which indicates that the rough morphology with morphology period of 12 Å is optimal to reduce the flow resistance and improve heat transfer performance jointly. [ABSTRACT FROM AUTHOR]

Based on the molecular dynamics principle, the convective heat transfer of the fluid through nanochannel with various rough nanostructure morphologies is investigated. The influences of nanostructure free shear ratio, morphology period and nanostructure depth on the flow and heat transfer characteristics are probed. A comprehensive evaluation on the convective heat transfer in rough nanochannel considering the flow resistance is performed. The result shows that the temperature jump and velocity slip dominate the heat and momentum exchange between the channel wall and fluid. Under the weak wall-fluid interaction, the smaller the nanostructure free shear ratio, the better the heat transfer performance as well as drag reduction characteristic. In contrast, the smaller the nanostructure morphology period, the better the heat transfer performance, the greater the flow resistance. Therefore, the wall rough morphology with small free shear ratio and sparse nanostructures is conducive to heat transfer augmentation and drag reduction jointly. The deeper rough nanostructure groove is unfavorable to reduce the flow resistance. The combination of rough nanostructure morphology and weak wall-fluid interaction is crucial, which will bring about a favorable impact on the heat transfer and flow resistance in nanochannel. Specifically, the nanostructure free shear ratio with ϕ a = 0.1875 is a favorable rough morphology to obtain optimum heat transfer and drag reduction characteristics in nanochannel. • A comprehensive evaluation about nanoscale convective heat transfer is discussed. • Nanoscale heat transfer and flow drag are affected by rough nanostructure morphology. • Rough channel with weak wall-fluid interaction is beneficial to drag reduction. • Small shear free ratio is beneficial for heat transfer and drag reduction jointly. • ϕ a = 0.1875 is an optimum rough morphology for convective heat transfer. [ABSTRACT FROM AUTHOR]